534 J. JR. Kih'oe — Laterite and Bauxite in Germany. 



hard limestone, but in chalk will tend to produce by solution a con- 

 stantly widening and deepening area of weakness, above which the 

 superincumbent strata will sag and produce at length a deeply sunk 

 valley." 



In the discussion on the papers read at the Geographical Society 

 Dr. A. Strahan mentioned that "in Dorset whei'e dry valleys are 

 dissected by the cliffs it may be seen that the underlying chalk is 

 rotten and undergoing solution." This is perfectly true, but the 

 observation does not support Mr. 8picer's theory, as Dr. Strahan 

 seemed to suppose. The chalk under such valley-floors is decomposed 

 and disintegrated into a loose mass of chalky paste and rounded pellets 

 of chalk, which is evidently due to the solvent action of water perco- 

 lating down from the surface ; whereas on Mr. Spicer's solution -theory 

 the cliff-section of such a valley ought to show an underground channel 

 or fissure widened by the passage of water, and all the chalk above 

 this widened fissure should show signs of the disruption, sagging, and 

 subsidence which he postulates. 



The facts and arguments brought forward by Mr. Spicer and 

 Mr. Bennett afford ample proof that chemical solution by percolating 

 water has played an important part in the deepening of certain valleys, 

 but I cannot see any good basis for their view that these valleys were 

 initiated by solution, nor for Mr. Bennett's theoiy of the " upward 

 hydrostatic action of underground water." It should be mentioned, 

 however, that Mr. Bennett fully admits the former existence of clay- 

 covers and the co-operation of mechanical erosion in the process of 

 valley-making, so that his view is much more rational and scientific 

 than that of Mr. Spicer. 



To sum up, therefore, I think that the actual initiation of valleys 

 in Chalk districts must be ascribed to the influence of surface conditions 

 which have long since ceased to exist ; and that the special features 

 which they now present can be explained by the action of surface- 

 causes which are still visibly in operation, namely, landslips and 

 solution of the valley-floors. I cannot see that there is any difficulty 

 in accounting for the dry valleys of limestone districts, or any reason 

 for inventing a special theory of ' solution-valleys ' to account for them. 



I do not know the area described by Mr. Bennett, and consequently 

 I cannot discuss the origin and formation of its valleys, but I should 

 have thought that the phenomena which he describes were as easily 

 explained on the old theory of the valleys having swallowed the 

 surface-streams as on his new theory of the swallow-holes having 

 initiated the valleys. 



II. — On the Occuhbence and Origin of Lateeite and Bauxite in 



THE VOGELSBEEG. 

 By J. E. KiLROE, A.E.C.S.I., H.M. Geological Survey of Ireland. 

 IIECENT visit to Central Germany afforded the writer an 



A 



opportunity of studying the conditions under which the 

 Vogelsberg iron-ore and bauxite have been formed, and a brief 

 account of what was observed may assist in broadening the basis upon 



